A simple analysis of recent maritime disasters involving grounding of large vessels shows a need for a device that will warn the ships personnel of rocks and other sunken obstacles in their immediate surroundings. Most noteworthy are the recent Exxon Valdez oil spill in Alaska and the Queen Elizabeth II grounding on an uncharted rock on the Connecticut shores. In both those cases, the personnel on the bridge could have benefited from an alarm that would warn against rocks or other such obstacles in the vicinity. It would alarm the crew and demand attention and reevaluation of the ships location. If the alarm indicates the direction of the threat, ship's crew or even an automated steering mechanism could prevent the grounding or reduce the impact. It is also noted that many obstacles large and massive enough to cause damage to sizable ships are frequently in groups. Therefore, a warning of a rock where one should not be is likely to cause the crew to reevaluate its position, slow down, or take other preventive measures.
The methods of underwater object detection by sonic echoes are common and well established and described by such as U.S. Pat. No. 3,740,705. Other range finding and scanning devices have been registered, such as U.S. Pat. No. 3,886,487, and specific transducers for primarily horizontal detection have been described in patents such as U.S. Pat. No. 5,142,505. Those patents describe scanning sonar transducers, method of overcoming wave clutter, and phased array transducer. However, no art was found to deal with an envelope type protection combined with a directionally adjusted alarm range, and logging capacity. In addition, most prior art, such as U.S. Pat. Nos. 3,740,705 and 3,886,487 relate to increasing accuracy of the detection system. Numerous patents have described methods of guidance of vehicles using sonar, such as U.S. Pat. No. 4,920,520 and many methods have been devised to increase accuracy and resolution of detection by different phasing methods and other such means.